1. Field of the Invention
The invention relates to an internal combustion engine having a cylinder head with a plurality of independent cooling water passages.
2. Description of Related Art
In an internal combustion engine, since it is difficult to form a block water jacket between cylinder bores in a high-temperature cylinder block, a inter-bore cooling water passage provided between cylinder bores, which is made of a drilled hole or the like, is formed between cylinder bores, and cooling water is introduced from a block water jacket into the inter-bore cooling water passage.
An internal combustion engine is disclosed, in which a block cooling water passage is communicated with an upper stage water jacket in a cylinder head through a inter-bore cooling water passage in order to cool a part between cylinder bores effectively (for example, Japanese Patent Application Publication No. 2002-168147 A (JP 2002-168147 A)).
In the internal combustion engine, after a lower part of the cylinder head, which faces a high-temperature combustion chamber, is cooled by a lower stage water jacket, cooling water in the lower stage water jacket is supplied to the upper stage water jacket.
Therefore, by leading the inter-bore cooling water passage to the upper stage water jacket having lower pressure than that of the lower stage water jacket, differential pressure between the block cooling water passage and the upper stage water jacket is increased, and thus a flow rate (flow velocity) in the inter-bore cooling water passage is increased, thereby improving cooling performance between cylinder bores.